En route to destruction: the evolution in composition of ices in comet D/2012 S1 (ISON) between 1.2 and 0.34 AU from the sun as revealed at infrared wavelengths
| Autor: | Ronald J. Vervack, Erika L. Gibb, N. Dello Russo, Michael A. DiSanti, Geoffrey A. Blake, Geronimo L. Villanueva, M. J. Mumma, Lucas Paganini, Adam J. McKay, Karen J. Meech, J. V. Keane, Boncho P. Bonev |
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| Jazyk: | angličtina |
| Rok vydání: | 2016 |
| Předmět: |
Physics
Astrochemistry 010504 meteorology & atmospheric sciences Infrared Comet Mean value Analytical chemistry Infrared spectroscopy Astronomy and Astrophysics Astrophysics 01 natural sciences Water production Wavelength Space and Planetary Science 0103 physical sciences Spectroscopy 010303 astronomy & astrophysics 0105 earth and related environmental sciences |
| Popis: | We report production rates for H2O and eight trace molecules (CO, C_2H_6, CH_4, CH_3OH, NH_3, H_2CO, HCN, C_2H_2) in the dynamically new, Sun-grazing Comet C/2012 S1 (ISON), using high-resolution spectroscopy at Keck II and the NASA IRTF on 10 pre-perihelion dates encompassing heliocentric distances R_h = 1.21–0.34 AU. Measured water production rates spanned two orders of magnitude, consistent with a long-term heliocentric power law Q(H_2O) ∝ R_h^(-3.1±0.1). Abundance ratios for CO, C_2H_6, and CH_4 with respect to H_2O remained constant with R_h and below their corresponding mean values measured among a dominant sample of Oort Cloud comets. CH_3OH was also depleted for R_h > 0.5 AU, but was closer to its mean value for R_h ≤ 0.5 AU. The remaining four molecules exhibited higher abundance ratios within 0.5 AU: for R_h > 0.8 AU, NH_3 and C_2H_2 were consistent with their mean values while H_2CO and HCN were depleted. For R_h < 0.5 AU, all four were enriched, with NH_3, H_2CO, and HCN increasing most. Spatial profiles of gas emission in ISON consistently peaked sunward of the dust continuum, which was asymmetric antisunward and remained singly peaked for all observations. NH_3 within 0.5 AU showed a broad spatial distribution, possibly indicating its release in the coma provided that optical depth effects were unimportant. The column abundance ratio NH_2/H_2O at 0.83 AU was close to the "typical" NH/OH from optical wavelengths, but was higher within 0.5 AU. Establishing its production rate and testing its parentage (e.g., NH_3) require modeling of coma outflow. |
| Databáze: | OpenAIRE |
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